I'm building a new flower/plant bed and need some advice on a border/barrier to keep out the grass. I'd like to use those bricks that have one curved end that nest into one another. But I've heard that to have a successful barrier against grass that you need something that goes at least 6 inches into the ground. Bricks are not that thick. But I've seen them in other people's yards and they seem, at least to my untrained eye, to be successful at the job. The alternative is that I have some of that black plastic barrier stuff that is 6 inches deep. But it is a pain in my neck to work with. Does anybody have any advice about this stuff? Thanks!